It is well known to construct sectional boilers by joining individual boiler flue sections together. The joints between the boiler flue sections were originally sealed with asbestos However, asbestos has been found to be environmentally hazardous and substitute materials have been sought.
One gasketing material which has been tried is glass fiber rope. However, that material was found not to provide an adequate seal in all instances, especially around the fire box in a gas-fired boiler.
Typically, asbestos gaskets would be applied to one of the mating faces of the sections before the sections were joined. Lengths of twenty to up to one hundred feet of the gasket had to be applied to a vertical mating surface of one of the two sections of the boiler being joined and held in position until the sections were secured together.